January 10, 2001
RELEASE: 01-02
CHANDRA LINKS PULSAR TO HISTORIC SUPERNOVA
New evidence from NASA's Chandra X-ray Observatory suggests
that a known pulsar is the present-day counterpart to a supernova
that exploded in 386 AD, a stellar explosion witnessed by Chinese
astronomers. If confirmed, this will be only the second known
pulsar to be clearly associated with a historic event.
In roughly the past 2,000 years, less than 10 reports of probable
supernovae have been archived, mostly by Asian astronomers. Until
now, the Crab Nebula has been the only pulsar whose birth is
associated with a historic event, the supernova of 1054 AD, making
it the only neutron star with a firm age.
"Determining the true ages of astronomical objects is notoriously
difficult," said Victoria Kaspi of the McGill University,
Montreal, Canada, "and for this reason, historical records of
supernova are of great importance."
These results were presented today by Kaspi and Mallory Roberts,
also of McGill University, at the American Astronomical Society
meeting in San Diego, CA. Also participating in the research were
Gautum Vasisht from NASA's Jet Propulsion Laboratory, Pasadena,
CA; Eric Gotthelf from Columbia University, New York City; Michael
Pivovaroff from Thermawave, Inc., Fremont, CA; and Nobuyuki Kawai
from the Institute of Physical and Chemical Research, Japan.
Scientists used Chandra to locate the pulsar exactly at the
geometric center of the supernova remnant known as G11.2-0.3. This
location provides very strong evidence that the pulsar, a neutron
star spinning 14 times per second, was formed in the supernova of
386 AD, making it 1,615 years old.
Since pulsars move rapidly once they are formed, Chandra's ability
to pinpoint the pulsar at the remnant's center implies the system
must be very young. "We believe that the pulsar and the supernova
remnant G11.2-0.3 are both likely to be left over from the
explosion seen by the Chinese observers over 1,600 years ago,"
said Roberts. "While this is exciting by itself, it also raises
new questions about what we know about pulsars, especially during
their infancies."
These questions arose when the research team of the Japanese
Advanced Satellite for Cosmology and Astrophysics (ASCA) applied
the present spin rate to current models to determine the pulsar's
estimated lifetime and compared it to the age of G11.2-0.3. The
result was an age of roughly 24,000 years -- far predating the
birth year of 386 AD. To explain this contradiction, the Chandra
team argues that this pulsar may have had approximately the same
spin rate today as it did at its birth. If true, this could have
important implications for conventional wisdom regarding pulsars,
which may be spinning more slowly than previously thought.
Between mid-April and mid-May in the year 386 AD, the sudden
appearance of a new star, presumably a supernova, was recorded by
Chinese observers in the direction of the sky now known as the
constellation of Sagittarius. In the 1970s, radio astronomers
discovered an expanding nebula of gas and high-energy particles,
called G11.2-0.3, believed to be the remnant of that explosion. In
1997, a team of X-ray astronomers used ASCA to discover a pulsar
in the same area of the sky.
Chandra observed G11.2-0.3 with the Advanced CCD Imaging
Spectrometer at two points in time: Aug. 6, 2000, and Oct. 15,
2000, for approximately 20,000 and 15,000 seconds respectively.
NASA's Marshall Space Flight Center in Huntsville, AL, manages the
Chandra program. The Smithsonian's Chandra X-ray Center controls
science and flight operations from Cambridge, MA. In addition to
their appointments at McGill, Kaspi is also affiliated with the
Massachusetts Institute of Technology, Cambridge, and Roberts is a
Quebec Merit Postdoctoral Fellow. The National Science Foundation
and NSERC (Canada) also provided funding for this work.
Associated images are available at:
http://chandra.nasa.gov
http://chandra.harvard.edu